RATIONALE Globally, over half of HIV-infected adults are women, and in the United States, 25% of all HIV/AIDS cases occur in women. Women often lack control over many available prevention measures, underscoring a critical need to enhance HIV prevention options for women. Pre-exposure prophylaxis (PrEP) is an HIV prevention strategy in which antiretroviral (ARV) drugs are used prior to potential HIV exposure to reduce the likelihood of infection. This strategy, which usually contains the drug tenofovir disoproxil fumarate (TDF), has recently shown promise, but efficacy data suggest room for improvement, particularly for women, in whom these data are conflicting. This study aims to prospectively examine ARV pharmacology and mucosal immunology in order to evaluate a novel PrEP strategy in women - blockade of HIV entry from its target cells at the mucosal surface using the CCR5 receptor antagonist maraviroc (MVC). These actions of CCR5 receptor antagonism, if validated, could lead to reduced HIV acquisition risk at more favorable dosing strategies than available for current PrEP. Knowledge of pharmacological modulation of mucosal immunity and HIV acquisition risk is fundamental to understanding, improving, and designing new PrEP strategies.